1. Field of the Invention
The present invention relates to an electrolytic solution for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery using the electrolytic solution.
2. Description of the Related Art
Nonaqueous electrolyte secondary batteries have been attracting attention as power sources for electronic instruments because the batteries each have a high energy density and a light weight. In particular, button type nonaqueous electrolyte secondary batteries have been widely utilized in portable electronic instruments such as portable telephones because of their small sizes.
In association with reductions in sizes of the electronic instruments and the like, the nonaqueous electrolyte secondary batteries have been implemented on the surfaces of substrates in recent years, and reflow soldering has been a mainstream method for the implementation.
Since the reflow soldering involves heating each of the nonaqueous electrolyte secondary batteries at about 250 to 260° C., such inconvenience as described below arises. That is, an electrolytic solution decomposes to cause a reduction in discharge capacity of each of the batteries, or the electrolytic solution leaks owing to bumping.
An electrolytic solution for a lithium secondary battery using an organic ether compound as a solvent has been conventionally proposed for enduring such reflow soldering at high temperatures (for example, Japanese Patent Application Laid-open No. Hei 11-26016).
By the way, the portable electronic instruments are each requested to have a sufficient discharge capacity in a wide range of temperature environments because the instruments are used outdoors as well as indoors.
However, a mere nonaqueous electrolyte secondary battery using an organic ether compound as a solvent and having heat resistance to endure the reflow soldering as described in Japanese Patent Application Laid-open No. Hei 11-26016 involves the following problem. That is, the voltage of the battery reduces in a low-temperature environment of 0° C. or less, and hence its discharge capacity is impaired.